1. Overhunting: Polynesian settlers, known as Māori, hunted moa for food and as a source of raw materials, such as feathers, bones, and skin. Hunting pressure from humans significantly reduced moa populations over time.
2. Habitat Modification: The arrival of Māori also brought deforestation, as they used fire to clear forests and create open areas for agriculture and hunting purposes. This process destroyed moa habitats, reducing their ability to find food and shelter.
3. Lack of Natural Defenses: Moa had evolved without any natural predators, as they had long been isolated in the unique ecosystem of New Zealand. This meant they were not adapted to the presence of humans and were easily hunted due to their large size and inability to fly.
4. Competition from Introduced Species: Polynesian settlers unintentionally introduced rats, dogs, and pigs to New Zealand. These introduced species preyed upon moa eggs, chicks, and even adult moa, leading to increased rates of mortality and a decline in population.
5. Climate Change: Although climate change at the time may have had an impact on their natural habitats, it's generally believed that the human factors mentioned above were the primary contributors to the extinction of moa.
Combined, these factors led to the rapid and dramatic decline of moa populations, resulting in their eventual extinction within a few hundred years of human settlement in New Zealand.